1. Field of the Invention
The present invention relates generally to the transmission of communication signals in a data storage system and, more particularly, to a system and method for transmitting communication signals between a controller and an automated robotic device in a tape cartridge library system.
2. Background
Current automated libraries for tape cartridges typically include arrays of multiple storage cells housing the tape cartridges, as well as multiple media drives. Multiple automated robotic devices may be used to move tape cartridges between the various storage cells and media drives within a library.
The use of multiple robotic devices in automated tape cartridge libraries raises various problems concerning the distribution of power to such robotic devices. More particularly, robotic devices used in automated tape cartridge libraries require power for operation thereof. In prior art automated tape cartridge libraries, the movement of the robotic devices is restricted by wire cable connections used for providing such power. That is, such cabling can prevent the robotic devices from crossing paths, or from continuous movement in one direction around the library without the necessity of ultimately reversing direction.
Such problems can be overcome through the use of brush/wiper technology. A robotic device traveling over a given route may use a power distributor such as fixed conductive strips to supply power to the robotic device, which itself is provided with brushes or wipers that contact the conductive strips in order to conduct power to the robotic device. Multiple brushes are preferably used on each robotic device to improve robustness and reliability. The integration of such conductive strips into the automated tape cartridge library, in conjunction with brush contacts provided on the robotic devices, allows for greater freedom of movement of the robotic devices, as well as for modular and extensible power distribution to robotic devices as library configurations change, or as libraries are connected in a modular fashion to form library systems.
Advantageously, the oppositely charged conductive layers of a power strip as described above can be used for transmitting communication signals between the robotic device and a host controller. In doing so, however, electromagnetic interference and unintended signal emissions can be a problem. This can be particularly true for power conductors that are quite long. Interference from radio, television, and other radio frequency (RF) electromagnetic radiation sources, whether or not intentionally emitted, can interfere with the communication signals modulated onto the power conductors. Such interference can cause data transmission errors and slow the maximum attainable rate of data transfer.
In that same regard, when communication signals are modulated onto a long power conductor, some of the RF energy can radiate through the air and interfere with nearby independent power conductors. If the nearby power conductors also contain modulated communication signals, harmful interference can result. The energy radiated by the modulated power conductors may also cause interference in radio and television broadcast bands, or other restricted RF bands. Such interference may be prohibited by government regulations.
Thus, there exist a need for an improved system and method for transmitting communication signals between a controller and a robotic device in a data storage library. Such a system and method would improve the electromagnetic compatibility (EMC) of brush and strip power distribution by the orientation of the power strip conductors. More particularly, such an improved system and method would employ positive and negative (ground) conductors preferably separated by a thin layer of insulating dielectric. The positive conductor would preferably be centered over the negative conductor, and the negative conductor would preferably be wider than the positive conductor in order to minimize fringing of the electric filed due to the modulated communication signal. The thin dielectric would minimize the xe2x80x9cloop areaxe2x80x9d of the conductors. The conductors themselves would be substantially flat and relatively thin in order to reduce their respective surface areas, thereby reducing xe2x80x9cskin effect.xe2x80x9d
Accordingly, the present invention provides an improved system and method for transmitting communication signals to and from an automated robotic device for use in a data storage library.
According to the present invention, then, in a data storage library having a plurality of cells for holding media cartridges for use in storing data, at least one media drive, a robotic device for transporting cartridges between the plurality of cells and the at least one media drive in the data storage library, and a controller for controlling the robotic device, a system is provided for transmission of communication signals between the controller and the robotic device. The system comprises a substantially planar electrical insulator having opposed first and second sides, a first substantially planer electrical conductor on the first side of the insulator for use in providing electrical power to the robotic device, the first conductor to be provided with an electrical charge and having a width, and a second substantially planar electrical conductor on the second side of the insulator for use in providing electrical power to the robotic device, the second conductor to be provided with an electrical charge opposite the electrical charge of the first conductor, the second conductor having a width. The system further comprises means for generating the communication signals for transmission between the controller and the robotic device on one of the first and second conductors, wherein the width of the second conductor is less than the width of the first conductor, and the second conductor is substantially centered on the second side of the insulator relative to the width of the first conductor to reduce fringing of an electromagnetic field resulting from a transmitted communication signal.
Also according to the present invention, in a data storage library having a plurality of cells for holding media cartridges for use in storing data, at least one media drive, a robotic device for transporting cartridges between the plurality of cells and the at least one media drive in the data storage library, and a controller for controlling the robotic device, a method is provided for transmission of communication signals between the controller and the robotic device, the method comprises providing a substantially planar electrical insulator having opposed first and second sides, providing a first substantially planer electrical conductor on the first side of the insulator for use in providing electrical power to the robotic device, the first conductor to be provided with an electrical charge and having a width, and providing a second substantially planar electrical conductor on the second side of the insulator for use in providing electrical power to the robotic device, the second conductor to be provided with an electrical charge opposite the electrical charge of the first conductor, the second conductor having a width. The method further comprises providing means for generating the communication signals for transmission between the controller and the robotic device on one of the first and second conductors, wherein the width of the second conductor is less than the width of the first conductor, and the second conductor is substantially centered on the second side of the insulator relative to the width of the first conductor to reduce fringing of an electromagnetic field resulting from a transmitted communication signal.
The above features, and other features and advantages of the present invention are readily apparent from the following detailed descriptions thereof when taken in connection with the accompanying drawings.